Liquid co2 passive subcooler

ABSTRACT

A heat exchanger associated with a duct for a first fluid including: a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; upper and lower duct portions in fluid communication with the central duct portion including stationary upper and lower duct portions and movable upper and lower duct portions having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion and enclosing the coiled conduit; and, a refrigeration apparatus and process including the same.

The present embodiments relate to utilizing energy contained in the gaseous refrigerant exhaust of a refrigeration chamber to pre-cool the liquid refrigerant entering the refrigeration chamber, resulting in a more efficient use of refrigerant.

Conventional refrigeration processes take various structural forms and utilize various cooling processes. One such process utilizes pressurized liquid refrigerants, such as CO₂, which are flashed upon entering the refrigeration chamber. When CO₂ is utilized, the flash typically results in about 48% solid CO₂ and about 52% gaseous CO₂, at a temperature of about −109° F. (−78.3° C.). The solid CO₂ contacts the items which are to be frozen and sublimates, thereby extracting heat from the item to be frozen. Other refrigerants, such as N₂, act in a similar manner, except that the phase change usually results in a mixture of liquid and gas, and the cooling effect is provided by the liquid refrigerant evaporating upon contact with the item to be frozen.

Regardless of the refrigerant used, gaseous refrigerant must be exhausted from the refrigeration chamber. Such gaseous refrigerant typically exits the refrigeration chamber at temperatures which are much lower than the temperature at which the pressurized liquid refrigerant enters the refrigeration chamber. The gaseous refrigerant thus expels into the outside environment much of the energy used to produce the pressurized liquid refrigerant. Therefore, in order to increase the efficiency of such refrigeration chambers, it is desirable to harness the energy of the gaseous exhaust in order to pre-cool the liquid refrigerant before it enters the refrigeration chamber.

A refrigeration process embodiment is provided which includes supplying liquid CO₂ into a refrigeration chamber, flashing the liquid CO₂ into gaseous CO₂ and solid CO₂ to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO₂ from the refrigeration chamber, wherein the liquid CO₂ passes through a tube-side of a shell-and-tube heat exchanger prior to entering the refrigeration chamber, and the gaseous CO₂ passes through a shell-side of the shell-and-tube heat exchanger after exiting the refrigeration chamber, thereby pre-cooling the liquid CO₂ prior to entering the refrigeration chamber.

A refrigeration apparatus embodiment is provided, which includes a refrigeration chamber; a liquid CO₂ storage apparatus for providing liquid CO₂ at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO₂ and CO₂ snow; and a heat exchanger disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO₂ prior to said flashing; wherein the heat exchanger is a shell-and-tube heat exchanger adapted to receive the liquid CO₂ through a tube-side inlet of the heat exchanger and to receive the gaseous CO₂ through a shell-side inlet of the heat exchanger after the gaseous CO₂ exits the refrigeration chamber, thereby pre-cooling the liquid CO₂ prior to the liquid CO₂ exiting a tube-side outlet of the heat exchanger and entering the refrigeration chamber.

In certain embodiments, the heat exchanger associated with a duct, such as an exhaust duct, may comprise a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions; a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.

In certain embodiments, the liquid CO₂ enters the tube side of the shell-and-tube heat exchanger at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the tube side of the shell-and-tube heat exchanger at about −25° F. (−31.7° C.) to about −5° F. (−20.6° C.). The pressure of the liquid CO₂ is substantially the same at entry and exit of the tube side of the shell-and-tube heat exchanger, in certain embodiments the pressure being from about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).

In a further embodiment, the gaseous CO₂ enters the shell side of the shell-and-tube heat exchanger at about −80° F. (−62.2° C.) and about atmospheric pressure and exits the shell side of the shell-and-tube heat exchanger at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.

In certain embodiments, the liquid CO₂ enters the at least one coiled tube of the heat exchanger at about −10° F. (−23.3° C.) to about 2° F. (−16.7° C.) and exits the at least one coiled tube of the heat exchanger at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.).

In a further embodiment, the gaseous CO₂ enters the shell of the heat exchanger at about −90° F. (−67.8° C.) and exits the shell of the heat exchanger at about −31° F. (−35.0° C.) to about −20° F. (−28.9° C.).

Greater than about 48%, and, in certain embodiments, at least about 55% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber.

In certain embodiments, the shell-and-tube heat exchanger is a one pass tube-side straight-tube heat exchanger, a two pass tube-side straight-tube heat exchanger, or a U-tube heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present embodiments, reference may be made to the following description taken in conjunction with the following drawings, of which:

FIG. 1 is a schematic block diagram of a refrigeration chamber using a liquid CO₂ subcooler.

FIG. 2 is a cross-sectional view of one embodiment of the liquid CO₂ subcooler.

FIG. 3 is a schematic cross-sectional view of another embodiment of the liquid CO₂ subcooler, utilizing a one pass tube-side straight-tube heat exchanger.

FIG. 4 is a schematic cross-sectional view of another embodiment of the liquid CO₂ subcooler, utilizing a two pass tube-side straight-tube heat exchanger.

FIG. 5 is a schematic cross-sectional view of another embodiment of the liquid CO₂ subcooler, utilizing a U-tube heat exchanger.

FIG. 6 is a schematic cross-sectional view of one embodiment of a heat exchanger for use as a liquid CO₂ subcooler, shown in subcooling mode.

FIG. 7 is a schematic cross-sectional view of the heat exchanger embodiment of FIG. 6, shown in bypass mode.

FIG. 8 is an elevational view of an embodiment of a heat exchanger for use as a liquid CO₂ subcooler, shown with a shell in the closed position from the latch-side of the shell, in subcooling mode.

FIG. 9 is an elevational view of the heat exchanger embodiment of FIG. 8, shown with the shell in the closed position from the hinge-side of the shell, in subcooling mode.

FIG. 10 is an elevational view of the heat exchanger embodiment of FIG. 8, shown with the shell in the open position, in bypass mode.

DESCRIPTION

A process is provided for utilizing the energy contained in the gaseous refrigerant exhaust of a refrigeration chamber in order to pre-cool the liquid refrigerant entering the refrigeration chamber, resulting in a more efficient use of refrigerant.

Provided is a refrigeration process comprising supplying liquid CO₂ into a refrigeration chamber, flashing the liquid CO₂ into gaseous CO₂ and solid CO₂ within the refrigeration chamber in order to create a cooling effect, and exhausting gaseous CO₂ from the refrigeration chamber, wherein the liquid CO₂ passes through a tube-side of a shell-and-tube heat exchanger prior to entering the refrigeration chamber, and the gaseous CO₂ passes through a shell-side of the shell-and-tube heat exchanger after exiting the refrigeration chamber, thereby pre-cooling the liquid CO₂ in the heat exchanger prior to entering the refrigeration chamber.

Heat exchangers are well known in the art of refrigeration, and any suitable type of heat exchanger may be used for the purposes of the present process, as determined by one of skill in the art, and may include various types of shell-and-tube heat exchangers.

The heat transfer resulting in the cooling or freezing which takes place within the refrigeration process results generally from sublimation of the solid CO₂ which contacts the items which are disposed within the refrigeration chamber. Thus, an increased amount of solid CO₂ will result in a more efficient cooling process. By pre-cooling the liquid CO₂ entering the refrigeration chamber, a greater percentage of the liquid CO₂ is converted into solid CO₂ via the flash, that is, having conversion to greater than 48% solid CO₂ (or “snow”).

In certain embodiments, the liquid CO₂ enters the tube side of the shell-and-tube heat exchanger at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the tube side of the shell-and-tube heat exchanger at about −25° F. (−31.7° C.) to about −5° F. (−20.6° C.). The pressure of the liquid CO₂ is substantially the same at entry and exit of the tube side of the shell-and-tube heat exchanger, in certain embodiments the pressure being from about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).

It is desirable that the pressure through the tube-side of the shell and tube heat exchanger remain substantially the same because a pressure drop through the tube-side may result in instability of the liquid stream, creating undesirable results such as solid CO₂ buildup within the tube-side of the heat exchanger.

In certain embodiments, the gaseous CO₂ enters the shell side of the shell-and-tube heat exchanger at about −80° F. (−62.2° C.) and about atmospheric pressure and exits the shell side of the shell-and-tube heat exchanger at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.

Greater than about 48%, and, in certain embodiments, at least about 55% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber, and the temperature of said resulting gaseous CO₂ and solid CO₂ is less than about −109° F. (−78.3° C.). This results in a more efficient use of CO₂, resulting in cost savings due to a reduction in the amount of CO₂ required to achieve a desired refrigeration temperature.

Referring now to FIG. 1, the refrigeration process apparatus 10 is comprised of a refrigeration chamber 24, a heat exchanger 20, a liquid CO₂ storage apparatus 22 and a recycle apparatus 26. The fresh CO₂ liquid 12 exits the liquid CO₂ storage apparatus 22 and enters the heat exchanger 20. Chilled CO₂ liquid 14 exits the heat exchanger 20 and enters the refrigeration chamber 24. Exhaust CO₂ gas 16 exits the refrigeration chamber 24 and enters the heat exchanger 20. Warmed CO₂ gas 18 exits the heat exchanger 20 and can be vented to the atmosphere 34, utilized in other processes 32, or recycled 28 by passing the warmed CO₂ gas through a recycle apparatus 26. If recycled, the CO₂ gas 30 exiting the recycle apparatus 26 is sent to the liquid CO₂ storage apparatus 22 to provide liquid CO₂ refrigerant.

Referring now to FIG. 2, the portion of the refrigeration process as herein described utilizes a heat exchanger 20. The fresh CO₂ liquid 12 enters the heat exchanger at the tube-side fluid inlet 42. The chilled CO₂ liquid 14 exits the heat exchanger at the tube-side outlet 44. The exhaust CO₂ gas 16 exiting the refrigeration chamber enters the heat exchanger at the shell-side inlet 46. The warmed CO₂ gas 18 exits the heat exchanger at the shell-side outlet 48. The warmed CO₂ gas 18 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant.

In further embodiments, the shell-and-tube heat exchanger may comprise at least one of a one pass tube-side straight-tube heat exchanger, a two pass tube-side straight-tube heat exchanger, or a U-tube heat exchanger.

FIG. 3 shows a one pass tube-side straight-tube heat exchanger 50 useful according to the present process. The fresh CO₂ liquid 12 enters the heat exchanger 50 at the tube-side inlet 52, passes through: a first tube sheet 62; the tube bundle 66 which utilizes straight tubes; and a second tube sheet 64; before exiting the heat exchanger as chilled CO₂ liquid 14 at the tube-side outlet 54. The chilled CO₂ liquid 14 is then flashed upon entering the refrigeration chamber (not shown). The exhaust CO₂ gas 16 which exits the refrigeration chamber enters the heat exchanger shell 68 at the shell-side inlet 56, passes around the baffles 60 in order to permit increased heat transfer from the liquid CO₂ to the gaseous CO₂, thereby chilling the liquid CO₂ stream. The warmed CO₂ gas 18 then exits the shell 68 at the shell-side outlet 58. The warmed CO₂ gas 18 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant. In the embodiment shown, the colder exhaust CO₂ gas is initially in a heat exchange relationship with chilled CO₂ liquid.

FIG. 4 shows a two pass tube-side straight-tube heat exchanger 70 useful according to the present process. The fresh CO₂ liquid 12 enters the heat exchanger 70 at the tube-side inlet 72, passes through: the upper portion of a first tube sheet 82; the upper portion of a tube bundle 86 which utilizes straight tubes; and the upper portion of a second tube sheet 84 into a plenum 89. The liquid CO₂ is then redirected by the plenum 89 through: the lower portion of the second tube sheet 84; the lower portion of the tube bundle 86; and the lower portion of the first tube sheet 82; before exiting the heat exchanger as chilled CO₂ liquid 14 at the tube-side outlet 74. The chilled CO₂ liquid 14 is then flashed upon entering the refrigeration chamber (not shown). The exhaust CO₂ gas 16 which exits the refrigeration chamber enters the heat exchanger shell 88 at the shell-side inlet 76, passes around the baffles 80 in order to permit increased heat transfer from the liquid CO₂ to the gaseous CO₂, thereby chilling the liquid CO₂ stream. The warmed CO₂ gas 18 then exits the shell 88 at the shell-side outlet 78. The warmed CO₂ gas 18 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant. In this embodiment, the liquid CO₂ can transfer heat to the colder exhaust CO₂ gas in two passes: upon entry into the heat exchanger as it passes through the upper portion of the tube bundle, and again before exiting the heat exchanger as it passes through the lower portion of the tube bundle.

FIG. 5 shows a U-tube heat exchanger 90 useful according to the present process. The fresh CO₂ liquid 12 enters the heat exchanger 90 at the tube-side inlet 92, passes through: a first tube sheet 102; the tube bundle 106 which utilizes U-tubes; and a second tube sheet 104; before exiting the heat exchanger as chilled CO₂ liquid 14 at the tube-side outlet 94. The chilled CO₂ liquid 14 is then flashed upon entering the refrigeration chamber (not shown). The exhaust CO₂ gas 16 which exits the refrigeration chamber enters the heat exchanger shell 108 at the shell-side inlet 96, passes around the baffles 100 in order to permit increased heat transfer from the liquid CO₂ to the gaseous CO₂, thereby chilling the liquid CO₂ stream. The warmed CO₂ gas 18 then exits the shell 108 at the shell-side outlet 98. The warmed CO₂ gas 18 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant.

FIG. 6 shows an embodiment of the present heat exchanger 200 in subcooling mode. A movable lower duct portion 206 and a movable upper duct portion 208 are in the open positions, while a valve 226 is in the closed position, causing diverted exhaust CO₂ gas 218 to pass through and among at least one coiled tube 212. Fresh CO₂ liquid, illustratively at −10° F. (−23.3° C.), enters the heat exchanger 200 at tube-side inlet 222 and passes through the at least one coiled tube 212 before exiting the heat exchanger 200 as chilled CO₂ liquid, illustratively at −35.7° F. (−37.6° C.), at the tube-side outlet 224. The chilled CO₂ liquid then flashes upon entering the refrigeration chamber (not shown). Exhaust CO₂ gas 214 which exits the refrigeration chamber via an exhaust duct (not shown) in communication with stationary lower duct portion 202 enters heat exchanger shell 210 at a shell-side inlet, such as stationary lower duct portion 202, thereby chilling the liquid CO₂ stream passing through the coiled tube 212. Warmed CO₂ gas 216 then exits the shell 210 through a shell-side outlet, such as stationary upper duct portion 204. The warmed CO₂ gas 216 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant.

By a “coiled tube” or “coiled conduit”, what is meant is any conduit which is oriented and/or constructed in such a manner as to allow the exhaust gas to move between and around multiple passes of the tubes or conduits as it travels through the shell, providing a heat-exchange relationship between the liquid within the tube or conduit and the gas moving through the shell.

FIG. 7 shows the heat exchanger 200 of FIG. 6 in bypass mode. The movable lower duct portion 206 and the movable upper duct portion 208 are in the closed positions, while valve 226 is in the open position, thus directing the exhaust CO₂ gas 220 to pass substantially through the central duct portion 228 and avoid the coiled tube 212. The shell 210 may be at least partially moved and/or removed so that the coiled tube 212 may be accessed from an exterior of the heat exchanger 200 for cleaning, sanitation and/or maintenance.

For example, the exhaust CO₂ gas 214 may contain any or all of the following contaminants, without limitation: entrained water in the form of ice crystals or water vapor as a result of mixing with environmental air within the refrigeration process/apparatus; entrained water from the products which are being cooled and/or frozen within the refrigeration process/apparatus; and/or food particles from the products which are being cooled and/or frozen within the refrigeration process/apparatus. If these or other contaminants are allowed to build-up on the heat exchange surfaces, such as the surfaces of the coiled tube 212, the heat exchange efficiency may be greatly reduced. By utilizing a shell which is at least partially movable and/or removable, such as the shell 210, the coiled tube 212 may be accessed to at least partially remove some or all of the contaminants, thereby restoring the heat exchange efficiency.

FIG. 8 shows an elevational view of an embodiment of the present heat exchanger 300, shown in the subcooling mode with a shell in the closed position from a latch-side of the shell. A movable lower duct portion 306 and a movable upper duct portion 308 are in the open positions, while a valve (not shown) within a central duct portion 328 is in the closed position, causing diverted exhaust CO₂ gas 318 to pass around the coiled tube 312. Fresh CO₂ liquid enters the heat exchanger 300 at the tube-side inlet 322 and passes through at least one coiled tube 312 before exiting the heat exchanger 300 as chilled CO₂ liquid at the tube-side outlet 324. The chilled CO₂ liquid then flashes upon entering the refrigeration chamber (not shown). Exhaust CO₂ gas 314, which exits the refrigeration chamber via an exhaust duct in communication with stationary lower duct portion 302, enters a heat exchanger shell, which consists of shell portions 310, 311, at the shell-side inlet, such as the stationary lower duct portion 302, thereby chilling the liquid CO₂ stream passing through the at least one coiled tube 312. Warmed CO₂ gas 316 then exits the shell 310 through the shell-side outlet, such as stationary upper duct portion 304. The warmed CO₂ gas 316 can be vented to the atmosphere, can be utilized in other processes, or can be recycled to provide liquid CO₂ refrigerant. Actuators, such as motors 330 and 332, displace or move the movable upper duct portion 308 and the movable lower duct portion 306, respectively. Latches 334 securely engage the shell portions 310, 311, although other means for movably (such as pivotably) securing or removably attaching the shell portions 310, 311 may be used.

For example, in certain embodiments, latches may be utilized on multiple portions of the shell in order to only partially, or perhaps completely, remove the shell from the heat exchanger so that the tube and/or conduits may be easily accessed for cleaning and/or maintenance. In another embodiment, such as that shown in FIG. 8, latches and hinges may be engaged with portions of the shell such that the shell may be opened, but remain engaged with the heat exchanger.

FIG. 9 is an elevational view of the heat exchanger 300 of FIG. 8 depicted from a hinge-side of the shell. FIG. 9 shows hinge 336 which releasably engages the portions 310, 311 on the side opposite from the latches 334, although other means for movably securing or removably attaching the shell portions 310, 311 may be used.

FIG. 10 is an elevational view of the heat exchanger of FIG. 8 depicted in bypass mode with the shell portions 310, 311 in the open position from the latch-side of the shell. The at least one coiled tube 312 is not depicted in this view for clarity. The actuator motors 330, 332 have moved the movable lower duct portion 306 and the movable upper duct portion 308 to their closed positions to engage the central duct portion 328, while the valve (not shown) within the central duct portion 328 is in the open position, thus allowing the exhaust CO₂ gas to pass substantially through the central duct portion 328. The shell portions 310, 311 may rotate about the hinge 336 to the open position, so that the at least one coiled tube 212 may be accessed from the exterior for cleaning, sanitation and/or maintenance.

The present refrigeration apparatus and process utilizes cold exhaust CO₂ gas (typically at about −90° F. (−67.8° C.)) flowing over the outside of a spiral-wound heat exchanger coil, such as that depicted in FIGS. 6 through 10 and discussed above, to subcool liquid CO₂ prior to use in the present apparatus/process. In the past, cold exhaust gas was usually wasted to the outside environment after leaving a refrigeration apparatus/process. By passing the cold exhaust CO₂ over the spiral-wound coil of the heat exchanger while passing warm CO₂ liquid (typically at about −10° F. (−23.3° F.)) through the spiral wound coil, such as in counter-flow operation, the incoming liquid CO₂ may be cooled from −10° F. (−23.3° F.) to about −36° F. (−37.8° C.), while the exhaust CO₂ gas may be warmed to about −31° F. (−35° C.). The heat exchange system may operate only while the refrigeration apparatus/process is operating, and therefore provides free cooling of the liquid CO₂ utilized as coolant in the refrigeration apparatus/process. The subcooling of the liquid CO₂ performed by the heat exchanger may raise the conversion rate of liquid CO₂ to solid CO₂ snow by up to 10%, or perhaps more. The higher conversion of liquid CO₂ to solid CO₂ snow may reduce CO₂ consumption by up to about 10%, or perhaps more.

Example

Liquid CO₂ is provided to the tube-side of the heat exchanger at 1.7° F. (−16.8° C.) and 300 psig (2,068 kPa). The specific enthalpy of the saturated liquid stream before entering the heat exchanger is 19.6 BTU/lb (45.6 kJ/kg). Exhaust CO₂ in gaseous form exiting the refrigeration chamber is provided to the shell-side of the heat exchanger at −80° F. (−62.2° C.) and about atmospheric pressure. The enthalpy of the gaseous stream before entering the heat exchanger is 139.1 BTU/lb (323.5 kJ/kg). The exhaust comprises 80% of the liquid CO₂ which enters the refrigeration chamber. This process warms the exhaust gas by 30° F. (−1.1° C.), therefore, the enthalpy of the gaseous stream exiting the heat exchanger would be 145 BTU/lb (337.3 kJ/kg) at a temperature of −50° F. (−45.6° C.).

The calculation to determine the subcooling achieved is: mass flow of the liquid stream times the change in enthalpy of the liquid stream is equal to mass flow of the gaseous stream times the change in enthalpy of the gaseous stream. Thus, where X will be the enthalpy of the liquid stream exiting the heat exchanger:

100×(19.6 BTU/lb−X)=80×(150.9 BTU/lb−145 BTU/lb)

Therefore, X is equal to 14.9 BTU/lb (34.7 kJ/kg), which corresponds to a liquid CO₂ temperature of approximately −8° F. (−22.2° C.) at 300 psig (2,068 kPa).

Without precooling, the heat of vaporization of saturated liquid CO₂ at 1.7° F. (−16.8° C.) and 300 psig (2,068 kPa) is 119.3 BTU/lb (277.5 kJ/kg). Utilizing the subcooler process according to the exemplified embodiment will result in a new heat of vaporization of 119.3 BTU/lb+change in enthalpy of the liquid CO₂ stream (19.6 BTU/lb−14.9 BTU/lb, or 4.7 BTU/lb). The new heat of vaporization of the now subcooled liquid stream will be 124.0 BTU/lb.

The increase in efficiency provided by the present process, utilizing a liquid CO₂ subcooler process can be determined by the following formula:

$1 - {\frac{{Non}\text{-}{Precooled}\mspace{14mu} {Heat}\mspace{14mu} {of}\mspace{14mu} {Vaporization}\mspace{14mu} (119.3)}{{Precooled}\mspace{14mu} {Heat}\mspace{14mu} {of}\mspace{14mu} {Vaporization}\mspace{14mu} (124.0)} \times 100\%}$

This results in an efficiency increase of 3.8%, which shows that less CO₂ can be utilized in the refrigeration process.

The foregoing is just one non-limiting example illustrating a potential freezing efficiency increase obtained with one embodiment of the subject process. The gains in freezing efficiency increase with the increase in the temperature differential of the exhaust gas through the heat exchanger.

A first embodiment of the subject apparatus and/or process includes a heat exchanger associated with a duct for a first fluid comprising: a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions; a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.

A second embodiment of the subject apparatus and/or process comprises a refrigeration apparatus comprising: a refrigeration chamber; a liquid CO₂ storage apparatus for providing liquid CO₂ at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO₂ and CO₂ snow; and the heat exchanger of the first embodiment, wherein the at least one conduit is disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO₂ prior to said flashing; the second fluid is liquid CO₂ flowing through the at least one conduit and the first fluid is gaseous CO₂ flowing through the shell after the gaseous CO₂ exits the refrigeration chamber, thereby pre-cooling the liquid CO₂ prior to the liquid CO₂ exiting the at least one conduit of the heat exchanger and entering the refrigeration chamber.

A third embodiment of the apparatus and/or process comprises a refrigeration process, comprising supplying liquid CO₂ into a refrigeration chamber, flashing the liquid CO₂ into gaseous CO₂ and solid CO₂ to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO₂ from the refrigeration chamber, wherein the liquid CO₂ is the second fluid passing through the at least one conduit of the heat exchanger of the first embodiment prior to entering the refrigeration chamber and the gaseous CO₂ is the first fluid passing through the shell of the heat exchanger after exiting the refrigeration chamber when the valve is in the closed position and the movable upper duct portion and lower duct portion are in their open positions, thereby pre-cooling the liquid CO₂ prior to entering the refrigeration chamber.

Any or all of the first, second or third embodiments may further include that, when the valve is in the open position, and the movable upper duct portion and the movable lower duct portion are in the closed positions, the first fluid passing through the duct passes substantially through the central duct portion.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that when the valve is in the closed position, and the movable upper duct portion and the movable lower duct portion are in their opened positions, the first fluid passing through the duct passes within the shell and around the at least one coiled conduit, thereby allowing heat to be transferred between the first fluid passing within the shell and the second fluid passing through the at least one conduit.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the valve is a quarter-turn valve.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the shell comprises at least two portions which are movably and/or removably engaged on at least one side of the heat exchanger, allowing the shell to be opened such that the at least one conduit can be accessed from exterior to the shell, and wherein the at least two portions are removably engaged on another side of the heat exchanger.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the liquid CO₂ enters the at least one conduit at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the at least one conduit at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.), wherein the pressure of the liquid CO₂ is substantially the same at entry and exit of the at least one conduit of the heat exchanger.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the pressure of the liquid CO₂ as it passes through the heat exchanger is about 239 psig (1,647 kPa) to about 300 psig (2,068 kPa).

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that the gaseous CO₂ enters the shell of the heat exchanger at about −90° F. (−67.8° C.) and about atmospheric pressure and exits the shell at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that greater than about 48% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, that at least about 55% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber.

Any or all of the preceding embodiments may further include, in addition to or in the alternative, opening the valve and closing the movable upper duct portion and the movable lower duct portion, whereby the gaseous CO₂ flows substantially through the central duct portion.

The preceding embodiment may further include opening the shell to access the at least one conduit.

The preceding embodiment may further include cleaning, sanitizing, and/or maintaining at least a portion of the at least one conduit.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result. 

1. A heat exchanger associated with a duct for a first fluid comprising: a central duct portion in fluid communication with the duct having an interior space and an exterior surface; a valve having opened and closed positions engageable within the interior space of the central duct portion; at least one coiled conduit for a second fluid positioned about at least a portion of the exterior surface of the central duct portion; an upper duct portion in fluid communication with the central duct portion comprising a stationary upper duct portion and a movable upper duct portion having opened and closed positions; a lower duct portion in fluid communication with the central duct portion comprising a stationary lower duct portion and a movable lower duct portion having opened and closed positions; and an at least partially movable and/or removable shell engaged with the stationary upper duct portion and the stationary lower duct portion, and enclosing the coiled conduit.
 2. The heat exchanger of claim 1, wherein when the valve is in the open position, and the movable upper duct portion and the movable lower duct portion are in their closed positions, the first fluid passing through the duct passes substantially through the central duct portion.
 3. The heat exchanger of claim 1, wherein when the valve is in the closed position, and the movable upper duct portion and the movable lower duct portion are in their opened positions, the first fluid passing through the duct passes within the shell and around the at least one coiled conduit, thereby allowing heat to be transferred between the first fluid passing within the shell and the second fluid passing through the at least one conduit.
 4. The heat exchanger of claim 1, wherein the valve is a quarter-turn valve.
 5. The heat exchanger of claim 1, wherein the shell comprises at least two pieces which are movably and/or removably engaged on at least one side of the heat exchanger, allowing the shell to be opened such that the at least one conduit can be accessed from exterior to the shell, and wherein the at least two portions are removably engaged on another side of the heat exchanger.
 6. A refrigeration apparatus comprising: a refrigeration chamber; a liquid CO₂ storage apparatus for providing liquid CO₂ at above atmospheric pressure to the refrigeration chamber for flashing into gaseous CO₂ and CO₂ snow; and the heat exchanger of claim 1, wherein the at least one conduit is disposed between and in fluid communication with the storage apparatus and the refrigeration chamber for receiving and chilling the liquid CO₂ prior to said flashing; the second fluid is liquid CO₂ flowing through the at least one conduit and the first fluid is gaseous CO₂ flowing through the shell after the gaseous CO₂ exits the refrigeration chamber, thereby pre-cooling the liquid CO₂ prior to the liquid CO₂ exiting the at least one conduit of the heat exchanger and entering the refrigeration chamber.
 7. A refrigeration process, comprising supplying liquid CO₂ into a refrigeration chamber, flashing the liquid CO₂ into gaseous CO₂ and solid CO₂ to provide a cooling effect within the refrigeration chamber, and exhausting gaseous CO₂ from the refrigeration chamber, wherein the liquid CO₂ is the second fluid passing through the at least one conduit of the heat exchanger of claim 1 prior to entering the refrigeration chamber and the gaseous CO₂ is the first fluid passing through the shell of the heat exchanger after exiting the refrigeration chamber when the valve is in the closed position and the movable upper duct portion and lower duct portion are in their open positions, thereby pre-cooling the liquid CO₂ prior to entering the refrigeration chamber.
 8. The process of claim 7, wherein the liquid CO₂ enters the at least one conduit at about −12° F. (−24.4° C.) to about 2° F. (−16.7° C.) and exits the at least one conduit at about −36° F. (−37.8° C.) to about −5° F. (−20.6° C.), wherein pressure of the liquid CO₂ is substantially the same at entry and exit of the at least one conduit of the heat exchanger.
 9. The process of claim 8, wherein the pressure of the liquid CO₂ as it passes through the heat exchanger is about 239 psig to about 300 psig.
 10. The process of claim 7, wherein the gaseous CO₂ enters the shell of the heat exchanger at about −90° F. and about atmospheric pressure and exits the shell at about −50° F. (−45.6° C.) to about −20° F. (−28.9° C.) and about atmospheric pressure.
 11. The process of claim 7, wherein greater than about 48% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber.
 12. The process of claim 7, wherein at least about 55% of the liquid CO₂ is converted into solid CO₂ upon flashing within the refrigeration chamber.
 13. The process of claim 7, further comprising opening the valve and closing the movable upper duct portion and the movable lower duct portion, whereby the gaseous CO₂ flows substantially through the central duct portion.
 14. The process of claim 13, further comprising opening the shell to access the at least one conduit.
 15. The process of claim 14, further comprising at least one of cleaning, sanitizing or maintaining at least a portion of the at least one conduit. 